Determinations of the plasma renin activity of renal venous and peripheral arterial blood, the renin content of aorta, and plasma aldosterone levels of adrenal venous blood will be made in spontaneously hypertensive rats (SHR), rats with renovascular hypertension, and normotensive control rats. Participation of the adrenals in the mechanism of hypertension is being investigated in SHR by means of adrenal enucleation. The effect of enucleation on the level of blood pressure during adrenal insufficiency and regeneration will be ascertained and correlated with the levels of plasma corticosterone and aldosterone. Also studies are being conducted on the effect of transplanting the whole adrenal gland or its enucleated portion to other regions of the body in SHR. Different levels of cholesterol will be maintained in hypertensive rats by dietary regimes with varying fat content to determine whether such levels influence the onset and development of atherosclerosis. Also drug therapy to reduce high blood pressure will be instituted in a group of obese SHR with the objective of retarding or preventing the development of premature atherosclerosis in these animals.